Glow discharge tube ignition circuit for electric discharge tube

ABSTRACT

Apparatus for starting and operating a gas discharge tube comprising a glow discharge starter connected to preheatable electrodes of the tube. An auxiliary circuit including a thyristor produces a voltage to ignite the glow discharge starter which then provides a path to heat the tube electrodes and subsequently aids in generating a voltage peak to ignite the discharge tube. The ignition voltage of the glow discharge starter is chosen to be higher than the AC supply voltage but lower than the voltage produced by the auxiliary circuit.

United States Patent Chermin Dec. 24, 1974 GLOW DISCHARGE TUBE IGNITION [56] References Cited CIRCUIT FOR ELECTRIC DISCHARGE UNITED STATES PATENTS TUBE 3,374,396 3/1968 Bell et al A. 3 IS/DIG. 5 [75] Inventor: Hubertus Mathias Jozef Chermin, I

Emmasingel, Eindhoven, Primary Examiner]ames B. Mullins Netherlands Attorney, Agent, or Firm--Frank Trifari; Bernard Franzblau [73] Assignee. U.S. Philips Corporation, New

Y k, N.Y. or 57 ABSTRACT [22] Wed: 1973 Apparatus for starting and operating a gas discharge [2] App]. No.: 340,052 tube comprising a glow discharge starter connected to preheatable electrodes of the tube. An auxiliary circuit including a thyristor produces a voltage to ignite I Fme'gn Application Priority Data the glow discharge starter which then provides a path Mill. i7, Netherlands to heat the tube electrodes and ubsequently aids in generating a voltage peak to ignite the discharge tube. Cl 315/99, 315/DIG- 315/DIG- 7, The ignition voltage of the glow discharge starter is 315/101 315/238 315/105 315/244 chosen to be higher than the AC supply voltage but Int. Cllower than the voltage produced the auxiliary [58] Field of Search... 3l5/DIG. 5, DIG. 7, 98-107, circuit 15 Claims, 1 Drawing Figure simple auxiliary circuit.

GLOW DISCHARGE TUBE IGNITION CIRCUIT FOR ELECTRIC DISCHARGE TUBE The invention relates to an arrangement provided with a gas and/or vapour discharge tube-having two electrodes, which arrangement has two input terminals intended to be connected to an alternating voltage source and which arrangement serves for igniting and supplying the discharge tube, the cold ignition voltage of the discharge tube being higher than the voltage of the alternating voltage source, the two input terminals being connected by a series arrangement of at least an inductor and the discharge tube, an auxiliary circuit comprising a controlled semiconductor rectifier being present by which with the arrangement switched on, but with the discharge tube not yet ignited a voltage is generated between the tube electrodes which voltage is higher than the voltage of the alternating voltage source.

The cold ignition voltage of a discharge tube, for example, a discharge lamp, is to be understood to mean the minimum required voltage to ignite this tube in the cold condition. The expression cold ignition voltage is sometimes used as the counterpart for the term hot ignition voltage. The hot ignition voltage of a discharge tube is then understood to mean the minimum voltage required to ignite this tube in the hot condition. ln lowpressure mercury vapour discharge lamps which are provided with pre-heated electrodes the cold ignition voltage (cold electrodes) is generally higher than the hot ignition voltage (hot electrodes). In, for example, high-pressure mercury vapour discharge lamps the reverse is generally the case, that is to say, the ignition voltage of the hot lamp is higher than that of the cold lamp.

A known arrangement of the kind mentioned in the preamble is described, for example, in Netherlands Patent Application No. 6501244. In this known arrangement the auxiliary circuit includes a thyristor which forms part of a voltage doubler which serves to provide the required ignition voltage for a discharge lamp.

A drawback of this known arrangement is that when the ignition voltage (or the re-ignition voltage) of the discharge lamp is very high, i.e. higher than can be realised with the auxiliary circuit including the controlled semiconductor rectifier, the lamp cannot be ignited at all or cannot be ignited immediately.

A further drawback in connection therewith is that when switching on the known arrangement during an.

interval at a fairly decreased supply voltage an ignition need not be performed in discharge lamps having an ignition voltage which is not too high because even then the auxiliary circuit'sometimes cannot generate a sufficiently high ignition voltage. In order to obtain higher voltages with the auxiliary circuit this circuit would have to become more complicated.

An object of the invention is to obviate or at least mitigate the said drawbacks in an arrangement of the kind described in the preamble while maintaining a According to the invention an arrangement provided with a gas and/or vapour discharge tube having two electrodes, which arrangement has two input terminals intended to be connected to an alternating voltage source and which arrangement serves for igniting and supplying a discharge tube having a, cold ignition voltage which is higher than the voltage of the alternating source, the two input terminals being connected by a series arrangement of at least an inductor and the discharge tube, and an auxiliary circuit including a controlled semiconductor rectifier being provided by which, with the arrangement switched on but with the discharge tube not yet ignited, a voltage is generated between the tube electrodes which is higher than the voltage of the alternating voltage source, and is characterized in that the electrodes of the discharge tube are connected together through a glow discharge starter whose ignition voltage is higher than the voltage of the alternating voltage source, but is lower than the voltage to be generated by the auxiliarycircuit.

An advantage of this arrangement according to the invention is that even in the case of fairly extreme circumstances, such as a very high ignition voltage (or reignition voltage) of the discharge tube or in the case of a fairly low value of the voltage of the alternating voltage source, for example, due to a decrease in the supply voltage, an ignition of the discharge tube can still be obtained.

In an arrangement according to the invention the auxiliary circuit provided with controlled semiconductor rectifier actually ensures a voltage which is increased relative to the alternating voltage source and to which the glow discharge starter responds. Shortly thereafter, the current through the inductor-in the series arrangement including the discharge tube will be interrupted abruptly due to the glow discharge starter contacts re-opening thereby producing a high voltage peak which will be present between the electrodes of the discharge tube. This voltage peak, which is higher than the voltage generated by the auxiliary circuit including the controlled semiconductor rectifier, causes the discharge lamp to ignite.

It is feasible that the ignition in the cold condition of I the discharge tube can be effected without the aid of the glow discharge starter, that is to say, with the aid of the auxiliary circuit only, and that the hot ignition voltage of this discharge tube can only be realized by the described combined action of the auxiliary circuit and the glow discharge starter. This case might occur, for example, in an arrangement which is provided with a high-pressure mercury vapour discharge lamp containing halides. The cold ignition is then effected by .the'

auxiliary circuit and the re-ignition (for example, when the lamp is extinguished but is still hot after an absence of several cycles of the alternating voltage source) by the auxiliary circuit and the glow discharge starter combined.

ln an arrangement according to the invention the electrodes may be either pre-heated or not pre-heated.

part of the series arrangement not bridged by the auxiliary circuit, the glow discharge starter is connected to those ends of the tube electrodes which are remote from the input terminals.

A first advantage of this preferred embodiment is that the glow discharge starter can realize both the preheating of the tube electrodes and the voltage peak between the tube electrodes for the purpose of igniting the tube.

It is true that the voltage-doubling combination of the capacitor and the controlled semiconductor rectifier according to the latter preferred embodiment is known per se from the previously mentioned Netherlands Patent Application No. 650l244, but an advantage relative to this Neverlands Patent Application is that in the preferred embodiment of the present invention no further wasted power is applied to the preheated electrodes after the ignition of the discharge tube.

A third advantage of this preferred embodiment is that it is also suitable for a discharge tube provided with pre-heated electrodes whose operating voltage is only slightly lower than that of the alternating voltage source, for example, different by a maximum of 40 volt. This may be explained as follows. In cases where the operating voltage of the discharge tube is only slightly lower than the voltage of the. alternating voltage source, for example, different by a maximum of 40 volt, the glow discharge starter can generally not be used in a simple manner in known circuits. The reason is that very stringent requirements would have to be imposed on the glow discharge starter. In fact, this starter must certainly ignite at the value of the voltage of the conventional alternating voltage source reduced by the normally expected voltage reductions of this source, while on the other hand the glow discharge starter must be extinguished at the slightly lower operating voltage of the discharge tube, which voltage deviates by only a few volts therefrom. The latter extinction is necessary to maintain the glow discharge starter inactive in the operating condition of the tube. In bulk manufacture of glow discharge starters such a very critical adjustment can hardly be realized. In the latter preferred embodiment the use of a glow discharge starter statisfying re- An advantage of this preferred embodiment is that the auxiliary circuit does not become active when the tube is removed from its holders because then the supply of current to the auxiliary circuit is interrupted because it can only be effected through this tube electrode.

It is feasible that both the glow discharge starter and the auxiliary circuit only bridge the discharge tube.

In a further advantageous embodiment according to the invention the auxiliary circuit bridges the series arrangement of the discharge tube and the inductor combined. An advantage of this preferred embodiment is that large voltage pulses which are generated when the contacts of the glow discharge starter are opened are quirements that are not too critical is also possible in the case of discharge tubes provided with pre-heated electrodes and operating at a voltage which is only slightly lower than the supply voltage. The reason is that the glow discharge starter must ignite at the higher voltage realized with the semiconductor rectifier while the glow discharge starter may be extinguished at the operating voltage of the discharge tube considerabl deviating therefrom. 1

his true that starters provided with a controlled semiconductor rectifier are known which are connected to the ends of pre-heated electrodes of a discharge tube remote from the alternating voltage source in which this starter is rendered inactive when the tube is ignited, but the two current directions were then often used in order to obtain a fast pre-heating of the electrodes. Such a double current direction excludes, however,'the possibility of using a simple voltage doubling arrangement with the aid of a capacitor and one current direction.

The auxiliary circuit may be connected, for example, to the two supply conductors leading from the input terminals to the discharge tube.

In an advantageous embodiment according to the invention one of the connection points of the auxiliary circuit including the controlled semiconductor rectifier is connected to one end of one of the pre-heated tube electrodes remote from the input terminals of the arrangement.

not present or are only present to a slight extent across the auxiliary circuit and consequently cannot damage the controlled semiconductor rectifier.

The controlled semiconductor rectifier of the auxiliary circuit may be rendered conducting, for example,

by means of a control pulse which is derived from a. transformer winding placed between the input terminals of the arrangement.

In a further advantageous embodiment according to the invention in which a control circuit of the controlled semiconductor rectifier forming part of the auxiliary circuit includes a second series arrangement of a second capacitor and a breakdown element with the v breakdwon element being connected to a control electrode of the controlled semiconductor rectifier, a third series arrangement of a first charge resistor and the second capacitor is connected in parallel with a branch of the auxiliary circuit icluding the controlled semiconductor rectifier. An advantage of the latter preferred embodiment is that the controlled semiconductor rectifier is rendered conducting in a very simple manner. In fact, the capacitor'is charged until the voltage of the breakdown element is achieved whereby the controlled semiconductor rectifier is brought to the conducting state. As is known, this rectifier becomes nonconducting again when the current therethrough becomeszero.

If it is desirable to renderthe auxiliary circuit inactive when the discharge tube is ignited, use may be made of, for example, a relay which responds to the lamp current and with which the auxiliary circuit can be rendered inactive.

In a further preferred embodiment according to the invention the second capacitor is shunted by the main electrode circuit of a transistor while a voltage derived from the tube current is applied between the base and a main electrode of said transistor so that the transistor conducts when the tube operates with the result that in the conducting condition of the transistor the voltage across the second capacitor is lower than the threshold voltage. of the breakdown element so that the controlled semiconductor rectifier does not then receive a control pulse.

An advantage of this preferred embodiment is that the auxiliary circuit can be rendered inactive in a very simple manner by actually short-circuiting the so-called second capacitor with the aid of the transistor so that control pulses cannot reach the controlled semiconductor rectifier.

In the latter preferred embodiment the base of the said transistor is preferably connected through at least a third capacitor to the emitter of said transistor and the connection between this base and the third capaciing across part of the inductor is utilized if the tube current flows through this inductor.

In an advantageous embodiment of an arrangement according to the invention which is intended to be connected to an alternating voltage supply of approximately 220 volts, the discharge tube is a low-pressure mercury vapour discharge lamp having an operating voltage of approximately 180 volts.

In this case the advantage is that this lamp can be rapidly ignited by means of the pre-heating current sup plied by the glow discharge starter while a very special glow discharge starter satisfying critical limits is not required because the ignition voltage of this glow dis charge starter, due to the action of the auxiliary circuit, may be considerably higher than the 180 volts operating voltage of this lamp. Without the presence of the auxiliary circuit the working interval of the glow discharge starter would lie between 220 volts minus approximately 5 percent supply voltage decrease on the one hand and 180 volts on the other hand.

The invention will be further described with reference to the accompanying drawing.-

The drawing shows an electrical circuit diagram of an arrangement according to the invention. Terminals 1 and 2 denote connection terminals for the arrangement which are intended to be connected to an alternating voltage supply of approximately 220 volts, 50 Hz. The terminal 1 is connected through a series arrangement of a capacitor 3, an inductor 4 and a discharge tube 5 to the terminal 2. The discharge tube 5 is provided with pre-heated electrodes 6 and 7. It is a low-pressure mercury vapour discharge lamp having an operating voltage of approximately 180 volts. An auxiliary circuit 9 is connected to a connection point 8 between the ca pacitor 3 and the inductor 4. The other side of this auxiliary circuit 9 is connected to a point 10 located on the side of the pre-heating electrode 7 of the discharge tube 5 remote from the supply terminal 2. Part of the auxiliary circuit 9 is connected to a tap l l on the inductor 4. Viewed from point 10 the first component in the auxiliary circuit 9 is a diode 12. Beyond diode 12 the circuit branches out into a parallel arrangement of a resistor 13 and a controlled semiconductor rectifier 14 on the one hand and a charge resistor 15 and a capacitor 16 on the other hand. The junction of the resistor 15 and the capacitor 16 is connected to a breakdown element 17. The other side of this breakdown element is connected to the control electrode of the controlled semiconductor rectifier (a thyristor) 14. The junction of the threshold element 17 and the control electrode of the thyristor 14 is furthermore connected through a resistor 18 to the cathode l4. Theside of the capacitor 16 remote from the resistor 15 is likewise connected to this cathode of the thyristor 14. This side of the capacitor 16 is also connected to the junction 8. The junction of the resistor 15 and the capacitor 16 is also connected through a resistor 19 to the collector of a transistor 20. The emitter of this transistor 20 is connected to the cathode end of the thyristor 14. The base of said transistor 20 is connected through a resistor 21 and a capacitor 22 to the emitter of this transistor. The connection between the resistor 21 and the capacitor'22 is connected through a subsequent resistor 23 and a diode 24 to the tap 11 on the inductor 4. A glow discharge starter 25 is connected to the side of the preheated electrode 6 remote from the supply terminal 1 and to the point 10.

The operation of the circuit described is as follows. When the alternating voltage of 220 volts, Hz is applied across the terminals 1 and 2 the capacitor 16 will be charged to a certain extent through the circuit 2, 7, l0, 12, 15, 16, 8, 3, 1. When the voltage across the capacitor has reached the threshold voltage of the disc breakdown element 17, the capacitor 16 will be discharged through this diac and provide a pulse for the control electrode of the thyristor 14. This thyristor thereupon becomes conducting. Subsequently a current will flow through the circuit 2, 7, 10, 12, l3, l4, 8, 3 to input terminal 1. The latter current will charge the capacitor 3 to a certain extent. When this charge has been only low during the first half cycle this capacitor will be further charged during a subsequent odd half cycle of the alternating voltage between the terminals 2 and 1. This means that a voltage which is slightly higher than the supply voltage, namely a supply voltage increasing to approximately double the peak value will be present between the electrodes 6 and 7 during the subsequent even half cycles. The glow discharge starter 25 then ignites. The heat evolved thereby in the glow discharge starter causes the bimetal electrode to curve so that the contacts reach each other and a connection is established in the circuit 1, 3, 4, 6, 25, 10, 7 to terminal 2. The preheating current which brings the electrodes 6 and 7 to the emission temperature then flows through this closed circuit. Some time after the contacts of the glow discharge starter 25 are closed they will open again because substantially no heat is evolved any longer in this glow discharge starter. The resultant voltage peak in the inductor 4 will appear across the tube 5 and thereupon this tube will ignite. When this is not effected for the first time, the glow discharge starter will undergo a subsequent similar starting procedure. When a current starts to flow through the circuit 1, 3,4 etc. by closure of the glow discharge starter contacts, a voltage is developed across the part 11, 8 of the inductor which charges the capacitor 22 through the diode 24, the resistor 23, the capacitor 22 and the point 8. This charge brings the transistor 20 from the originally non-conducting condition to the conducting condition. The voltage across the capacitor 16 is then greatly reduced and is brought to a level below the threshold voltage of the diac 17. The supply of control pulses to the thyristor 14 is consequently interrupted so that this auxiliary circuit is rendered inactive thereby. When't he discharge tube 5 is also ignited, the voltage between the electrodes 6 and 7 will be reduced to the operating voltage of this tube, namely approximately volts, whereupon the glow discharge starter is extinguished. In the situation then obtained the circuit represented by input terminal 1, capacitor 3, inductor 4, electrode 6, tube 5, electrode 7 and terminal 2 is important. The lamp then operates capacitively stabilized at the 220 volts supply. In one embodiment the ignition voltage of the glow discharge starter was 300 volts effective. This voltage was amply reached by the voltage doubling circuit of thyristor l4 and capacitor 3. The capacitor 3 had a capacitance of approximately 4.9 p. Farad, the inductor 4 had an inductance of approximately one Henry. The part of the inductor between 8 and 11 and the other part of the inductor had a winding ratio of approximately 1 10. The resistors 13, 15, 18, 19, 21 and 23 had resistances of 30 ohms, 33 KOhms, l KOhm, l kOhm, l8 kOhms and 68 Ohms, respectively. The capacitors 16 and 22 had a capacitance of 0.1 u Farad and l p. Farad, respectively.

An advantage of the circuit described is that the glow discharge starter 25 need not satisfy very critical requirements and that in addition the lamp ignites within three seconds. Further advantages are that the auxiliary circuit 9 and the glow discharge starter 25 are rendered inactive during the operating condition of the lamp 5 and that neither of the auxiliary circuits 9 and 25 can be switched on in the event that the lamp 5 is removed from its lamp holders.

The components 12 to 25 inclusive, see the part of the Figure within the broken lines, may be present, if desired, in one structural unit (an auxiliary starter).

What is claimed is:

1. An arrangement for starting and operating an electric discharge tube having two electrodes comprising, two input terminals adapted tobe connected to an alternating voltage source, the cold ignition voltage of the discharge tube being higher than the voltage of the alternating voltage source, an inductor, means connecting the series arrangement of the inductor and the discharge tube across said two input terminals, auxiliary circuit means including a controlled semiconductor rectifier coupled to the input terminals and to the tube electrodes for generating ignition voltage between the tube electrodes before the tube is ignited of a value which is higher than the voltage of the alternating voltage source, and means connecting the electrodes of the discharge tube together through 'a glow discharge starter whose ignition voltage is higher than the voltage of the alternating voltage source and lower than the voltage to be generated by the auxiliary circuit means.

2. An arrangement as claimed in claim 1 wherein the auxiliary circuit means bridges at least a part of said series arrangement and the two electrodes of thedischarge tube are preheated electrodes and the series arrangement'connected to the input terminals also includes a capacitor which is present in a part of the series arrangement not bridged by the auxiliary circuit means, characterized in that the glow discharge starter is connected to those ends of the tube electrodes which are remote from the input terminals.

3. An arrangement as claimed in claim 2 wherein the auxiliary circuit means including the controlled semiconductor rectifier is connected to one end of one of the tube electrodes remote from the input terminals of the arrangement.

4. An arrangement as claimed in claim 1 wherein the auxiliary circuit means bridges the series arrangement of the tube and the inductor.

5. An arrangement as claimed in claim 2 in which a control circuit of the controlled semiconductor rectifier includes a second series arrangement of a second capacitor and a voltage breakdown element with the breakdown element connected to a control electrode of the controlled semiconductor rectifier, and means connecting a third series arrangement of a first resistor and the second capacitor in parallel with a branch ofthe auxiliary circuit means including the controlled semiconductor rectifier.

6. An arrangement as claimed in claim 5, in which the second capacitor is shunted by the main electrode circuit of a transistor, characterized in that a voltage derived from the tube current is applied between the base and a main electrode of said transistor so that the transistor conducts when the tube operates, the voltage across the second capacitor then being lower than the threshold voltage of the breakdown element so as to inhibit the passage of a control pulse to the controlled semiconductor rectifier. I

7. An arrangement as claimed in claim 6, wherein the base of the transistor is connected through a third capacitor to the emitter of said transistor and the connec tion between said base and the third capacitor is connected through a diode to a tap on the inductor.

8. An arrangement as claimed in claim 2 adapted for connection to an alternating voltage source of approximately 220 volts, characterized in that the discharge tube is a low-pressure mercury vapour discharge lamp having an operating voltage of approximately volts.

9. Apparatus for starting and operating an electric discharge tube from a source of alternating current comprising, a pair of input terminals for connection to said source, an inductor, means connecting the inductor and the tube in series circuit across the input terminals, auxiliary circuit means having a first branch in.- cluding a controlled semiconductor rectifier connected in shunt with a part of said series circuit and operative to generate a voltage'across the tube electrodes before the tube is ignited of a value higher than the voltage of the alternating current source, said tube having a pair of electrodes defining a discharge path in the tube and a cold ignition voltage that is higher than the voltage of the alternating current source, a glow discharge starter having an ignition voltage higher than the voltage of the alternating current source and lower than the voltage generated by the auxiliary circuit means, and means connecting the glow discharge starter across the tube electrodes so as to provide a current path from the input terminals through the tube electrodes and the glow discharge starter than shunts the tube discharge path. 7

10. Apparatus as claimed in claim 9 further comprising a capacitor connected in series with the inductor and the tube across the input terminals so that the capacitor is charged via the controlled semiconductor rectifier during alternate half cycles of the alternating current source to produce a voltage multiplier effect.

11. Apparatus as claimed in claim 10 wherein the auxiliary circuit means is connected between one tube electrode and a junction between the capacitor and the inductor.

12. Apparatus as claimed in claim 9 wherein the auxiliary circuit means includes a second branch in parallel with the first branch and including a capacitor with a charge path coupled to said input terminals, and a voltage breakdown element coupling the capacitor to the control electrode of the controlled semiconductor rectifier for periodically applying a trigger pulse thereto during alternate half cycles of the alternating current source.

13. Apparatus as claimed in claim 12 further comprising a switching element connected in shunt with the tor rectifier during alternate half cycles of the alternating current source.

15. Apparatus as claimed in claim 9 wherein said first branch of the auxiliary circuit means is connected between one tube electrode and one input terminal such that the one tube electrode completes the current path from the input terminals to the first branch.

5 UNITED STATES PATENT owner CETEFECATE QEQTIQN Patent No. 3857060 Dated December 24, 1974 Inventor(s) Hubertus M. J. Chermin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[- IN THE SPECIFICATIONS 1 column 6, lines 20-21, cancel "When this charge has been only low" and insert -If the capacitor receives a relatively small chargecolumn 6, line 21, cancel "this" and insert the--;

IN THE CLAIMS column 9, line 8, before "capacitor" insert -second--;

Signed and Sealed this twenty-ninth Day of July 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissimzvr qflalentx and Trademarks 

1. An arrangement for starting and operating an electric discharge tube having two electrodes comprising, two input terminals adapted to be connected to an alternating voltage source, the cold ignition voltage of the discharge tube being higher than the voltage of the alternating voltage source, an inductor, means connecting the series arrangement of the inductor and the discharge tube across said two input terminals, auxiliary circuit means including a controlled semiconductor rectifier coupled to the input terminals and to the tube electrodes for generating ignition voltage between the tube electrodes before the tube is ignited of a value which is higher than the voltage of the alternating voltage source, and means connecting the electrodes of the discharge tube together through a glow discharge starter whose ignition voltage is higher than the voltage of the alternating volTage source and lower than the voltage to be generated by the auxiliary circuit means.
 2. An arrangement as claimed in claim 1 wherein the auxiliary circuit means bridges at least a part of said series arrangement and the two electrodes of the discharge tube are preheated electrodes and the series arrangement connected to the input terminals also includes a capacitor which is present in a part of the series arrangement not bridged by the auxiliary circuit means, characterized in that the glow discharge starter is connected to those ends of the tube electrodes which are remote from the input terminals.
 3. An arrangement as claimed in claim 2 wherein the auxiliary circuit means including the controlled semiconductor rectifier is connected to one end of one of the tube electrodes remote from the input terminals of the arrangement.
 4. An arrangement as claimed in claim 1 wherein the auxiliary circuit means bridges the series arrangement of the tube and the inductor.
 5. An arrangement as claimed in claim 2 in which a control circuit of the controlled semiconductor rectifier includes a second series arrangement of a second capacitor and a voltage breakdown element with the breakdown element connected to a control electrode of the controlled semiconductor rectifier, and means connecting a third series arrangement of a first resistor and the second capacitor in parallel with a branch of the auxiliary circuit means including the controlled semiconductor rectifier.
 6. An arrangement as claimed in claim 5, in which the second capacitor is shunted by the main electrode circuit of a transistor, characterized in that a voltage derived from the tube current is applied between the base and a main electrode of said transistor so that the transistor conducts when the tube operates, the voltage across the second capacitor then being lower than the threshold voltage of the breakdown element so as to inhibit the passage of a control pulse to the controlled semiconductor rectifier.
 7. An arrangement as claimed in claim 6, wherein the base of the transistor is connected through a third capacitor to the emitter of said transistor and the connection between said base and the third capacitor is connected through a diode to a tap on the inductor.
 8. An arrangement as claimed in claim 2 adapted for connection to an alternating voltage source of approximately 220 volts, characterized in that the discharge tube is a low-pressure mercury vapour discharge lamp having an operating voltage of approximately 180 volts.
 9. Apparatus for starting and operating an electric discharge tube from a source of alternating current comprising, a pair of input terminals for connection to said source, an inductor, means connecting the inductor and the tube in series circuit across the input terminals, auxiliary circuit means having a first branch including a controlled semiconductor rectifier connected in shunt with a part of said series circuit and operative to generate a voltage across the tube electrodes before the tube is ignited of a value higher than the voltage of the alternating current source, said tube having a pair of electrodes defining a discharge path in the tube and a cold ignition voltage that is higher than the voltage of the alternating current source, a glow discharge starter having an ignition voltage higher than the voltage of the alternating current source and lower than the voltage generated by the auxiliary circuit means, and means connecting the glow discharge starter across the tube electrodes so as to provide a current path from the input terminals through the tube electrodes and the glow discharge starter than shunts the tube discharge path.
 10. Apparatus as claimed in claim 9 further comprising a capacitor connected in series with the inductor and the tube across the input terminals so that the capacitor is charged via the controlled semiconductor rectifier during alternate half cycles of the alternating current source to produce a voltage muLtiplier effect.
 11. Apparatus as claimed in claim 10 wherein the auxiliary circuit means is connected between one tube electrode and a junction between the capacitor and the inductor.
 12. Apparatus as claimed in claim 9 wherein the auxiliary circuit means includes a second branch in parallel with the first branch and including a capacitor with a charge path coupled to said input terminals, and a voltage breakdown element coupling the capacitor to the control electrode of the controlled semiconductor rectifier for periodically applying a trigger pulse thereto during alternate half cycles of the alternating current source.
 13. Apparatus as claimed in claim 12 further comprising a switching element connected in shunt with the capacitor and responsive to the flow of tube current to limit the capacitor voltage to a value below the trigger level of the breakdown element thereby to inhibit said trigger pulses when the discharge tube is conductive.
 14. Apparatus as claimed in claim 12 further comprising a second capacitor connected in series with the inductor and the tube across the input terminals so that the capacitor is charged via the controlled semiconductor rectifier during alternate half cycles of the alternating current source.
 15. Apparatus as claimed in claim 9 wherein said first branch of the auxiliary circuit means is connected between one tube electrode and one input terminal such that the one tube electrode completes the current path from the input terminals to the first branch. 